1. Field of the Invention
The present invention relates to an apparatus and a method for feeding printing plate precursors, wherein printing plate precursors are accommodated in a stack, and an uppermost printing plate precursor is removed from the stack such that it is kept in a state of substantially parallel to lower plates.
2. Description of the Related Art
A technique has been developed, wherein a printing plate precursor such as a photopolymer plate having a photosensitive layer (for example, a photopolymerization layer) provided on a support is used and an image is directly recorded on the photosensitive layer of the printing plate precursor using a laser beam or the like. There is an automatic exposure apparatus for printing plate precursors.
In such a technique, printing plate precursors have to be transferred one after another in order for image recording on a printing plate precursor to be performed rapidly. For this purpose, a plurality of the printing plate precursors and interleaf papers for protecting the printing surface of the printing plate precursors are accommodated in a cassette in which the plates and the interleaf papers are alternately stacked. The plates and the interleaf papers are kept in this condition at a predetermined position, then the printing plate precursors are automatically removed one-by-one by a suction-adhering apparatus including suction nozzles and fans, and then transferred to the exposure portion.
Further, the cassette in which the printing plate precursors are accommodated is provided with a separation plate, which corresponds with both corners of the upper ends of the accommodated printing plate precursors. When a printing plate precursor is removed from the cassette by the suction-adhering apparatus such as suction nozzles and fans, the separation plate engages with the printing plate precursor and causes the both corners of the upper end of the printing plate precursor to bend. Consequently, the printing plate precursor which is suction-adhered can be separated from the underlying printing plate precursor or the interleaf paper rapidly and removed.
In the prior art, a suction-adhering apparatus including suction nozzles and fans is provided in a feeding apparatus body. While, cassettes are detachable from the feeding apparatus body. A plurality of cassettes each accommodating printing plate precursors of different sizes are provided, and they are selected in accordance with need and mounted in the feeding apparatus body.
For this reason, the structure is such that even when the cassette is changed, the relative position of the suction-adhering apparatus with respect to the cassette basically corresponds in design. However, deviation of the position of the suction-adhering apparatus with respect to each cassette may occur due to differences in the printing apparatus.
Here, after suction nozzles of a suction-adhering apparatus suction-adheres a printing plate precursor, the nozzles must be raised to a position at which a separation plate can separate the plate properly.
This movement starts with the position of the suction-adhering apparatus as an initial position. The suction-adhering apparatus is provided in a unit capable of moving toward and away from the cassette, along with a plate sensor for detecting the uppermost printing plate precursor accommodated in the cassette. Therefore, the position of this unit is determined as the initial position.
The unit approaches the cassette from the initial position. Then, when the uppermost printing plate precursor is detected by the plate detecting sensor, approaching movement of the unit is stopped after movement of a predetermined amount after detection. At this point, the suction nozzles of the suction apparatus adheres to the plate surface, then the printing plate precursor can be suction-adhered by starting suctioning.
After this operation, the unit is moved in a direction away. From the cassette it is moved to a position which has been memorized as the most optimum point for the separating position. When the unit is driven by a pulse motor, the pulse number should be memorized.
However, as described above, when the relative position of the apparatus body with respect to the cassettes does not match, an optimum positioning can not be unconditionally determined.
For this reason, in the vicinity of the optimum separating position, the suction nozzles which suction-adhere a printing plate precursor is moved intermittently so as to secure the optimum position which is different each time.
This problem can be resolved to a certain extent by memorizing the optimum separating position of the suction nozzles as an initial value and using amending data to amend the initial value for each cassette. However, a separate apparatus for discriminating cassettes is needed. Further, if an error occurs in discriminating the cassettes, separating efficiency may decrease. As strict control of the operation is needed, control operation for an operator becomes complicated.
Further, even in the case where the cassettes are the same size the positioning error may be caused due to the member in which the cassette is mounted. In this case, the amending data is not useful.
The present invention has been devised in view of the above-described circumstances, and an object thereof is to achieve a sheet feeding apparatus for printing plate precursors by which at each feeding the optimum position of a suction-adhering apparatus can be determined and sheet-feeding with efficient separation can be reliably provided.
A first aspect of the present invention is an apparatus for feeding printing plate precursors, the apparatus comprising: a cassette which accommodates printing plate precursors in a stack, the cassette including a separation plate that engages with corners of the printing plate precursors for aiding to separate an uppermost printing plate precursor from underlying printing plate precursors; a suction unit including a suction member which suction-adheres to an uppermost printing plate precursor accommodated in the cassette, the suction unit being supported so as to be movable toward and away from the cassette; a driving device which moves the suction unit; a plate detecting sensor provided in the suction unit, the plate detecting sensor being positioned within a predetermined distance of a printing plate precursor using a suction surface of the suction member as a reference so as to detect a position of the uppermost printing plate precursor when the suction unit moves close to the printing plate precursor; a separating plate detecting sensor provided in the suction unit, the separating plate detecting sensor for detecting the separating plate or a member having a fixed relative position with respect to the separating plate before the plate detecting sensor detects the uppermost printing plate precursor; and a controlling device which controls the driving device on the basis of the detection by the plate detecting sensor and the separation plate detecting sensor to move the suction unit toward and away from the cassette while controlling timing of the suction member for removal of printing plate precursors.
According to the present invention, a suction unit is moved towards cassettes from the predetermined position. During this movement, a position, at which a separation plate is detected by a separation plate detecting sensor, is memorized. Further, a member whose relative position with respect to a separation plate is fixed, may be detected instead of direct detection of the separation plate.
A second aspect of the present invention is A method for feeding printing plate precursors from a cassette holding the printing plate precursors in a stack, the method comprising the steps of: determining the initial position of a movably mounted suction frame which suction adheres printing plate precursors to suction nozzles provided on the suction frame by application of reduced pressure to the suction nozzles; moving the suction frame toward the cassette using a pulse-controlled motor which when operated moves the suction frame away and towards the cassette; detecting a portion of the cassette with a first sensor; detecting a surface of an uppermost printing plate precursor in the stack in the cassette with a second sensor; reading a first drive controlling pulse number of the motor; and moving the suction frame further downward by a predetermined amount and stopping the frame at a position at which the suction nozzles adhere to the uppermost printing plate on the stack when reduced pressure is applied to the suction nozzles.
At this point, the suction unit continues the movement. During this movement, the uppermost printing plate precursor accommodated in the cassette is detected by the plate detecting sensor. Then, a suction-adhering member closely contacts the uppermost printing plate precursor by moving by the predetermined amount.
After a suction-adhering member closely contacts the printing plate precursor, the suction-adhering member is moved apart from a cassette. At this point, the suction-adhering unit is moved to the separation plate detecting position which was memorized previously, then the unit is stopped.
A separation plate detecting point of a separation plate detecting apparatus is defined as an optimum separating point when a suction-adhering member suction adheres to a printing plate precursor. Consequently, the uppermost printing plate precursor is separated from an underlying plate precursor reliably and transferred to the next process.
As described above, an optimum point for separating is determined and an efficient separation is provided by a proper detection of a separation plate detecting apparatus. Even if a cassette is changed, operation for rewriting amending data and the like is not needed.